Bowflex Select Tech Dumbbells contain patented technology that has revolutionized the exercise and fitness industry. They incorporate a patent pending locking system which enables you to specify the exact weight at which you wish to lift. The tumblers then fasten to the weight you have indicated and the bar pulls out of the docking mechanism with the correct weights securely fastened. Changing weight resistance involves only a simple turn of the dial, switching from 10 pounds thru 90 pounds has never been easier! The rapidity with which you can change weights makes sure your heart rate stays up, and your workout stays focused. Bowflex Select Tech Dumbbells reduce a typical 34 dumbbell set to just two dumbbells, providing incredible savings and space reduction for the perfect home workout purchase.